Add action to combine results of mutliple endpoints

[chriskapp]

I have just saw the Krakend API gateway and they have a feature to combine the results of multiple endpoints into one result s.

We could also create an action which combines the results of multiple endpoints and returns a single response. In the background this should use the HTTP-Processor. Maybe we could also provide a way to cache those responses. It would be easy to create an action with PHP but probably it would be useful if we have such an action which can be configured.

[chriskapp]

We have created an action at the HTTP adapter s. https://github.com/apioo/fusio-adapter-http which handles this case. The new version of the HTTP adapter is then included at the next release.